With continuous development of mobile communications technologies, increasingly high bandwidth required for data transmission imposes a higher requirement on an operating bandwidth of a receiver. The receiver is a device used for converting a radio frequency signal to a digital baseband signal. A conventional receiver includes a superheterodyne receiver and an I/Q (in-phase/quadrature) demodulator receiver. A structure of the superheterodyne receiver is shown in FIG. 5(A). A digital baseband signal is output after a radio frequency signal passes through a filter, an amplifier, a frequency mixer, and a detector. The frequency mixer is configured to perform frequency mixing on a received signal and a signal generated by an oscillator, to obtain an intermediate frequency signal. Because channel bandwidth of the frequency mixer in the receiver generally does not exceed twice the center frequency of the intermediate frequency signal, and the center frequency of the intermediate frequency signal generally does not exceed 500 MHz, an operating bandwidth of the receiver is limited by the channel bandwidth of the frequency mixer and cannot reach a GHz magnitude. A structure of the I/Q demodulator receiver is shown in FIG. 5(B). A digital baseband signal is output after a radio frequency signal passes through a filter, an amplifier, an I/Q demodulator, and a detector. The I/Q demodulator is configured to perform frequency conversion on a received signal. Because channel bandwidth of the I/Q demodulator does not exceed 500 MHz, the operating bandwidth of the receiver is limited by the channel bandwidth of the /IQ demodulator and cannot reach a GHz magnitude.
A direct radio frequency (Direct RE) receiver is a new-generation receiver. A structure of the direct radio frequency receiver is shown in FIG. 5(C). A digital baseband signal is output after a radio frequency signal passes through a filter, an amplifier, an analog to digital converter, and a converter. The direct radio frequency receiver directly performs high-speed analog-to-digital conversion on the radio frequency signal without a need of performing frequency mixing or frequency conversion; therefore, an operating bandwidth of the direct radio frequency receiver depends on only sampling bandwidth of the analog-to-digital conversion, so that the operating bandwidth of the entire receiver can be increased by increasing the sampling bandwidth, so as to reach the GHz magnitude. The analog to digital converter of the direct radio frequency receiver uses a high-speed analog to digital converter (ADC), and requires that sampling bandwidth of the high-speed ADC is much higher than the operating bandwidth of the direct radio frequency receiver, for example, for an operating bandwidth of 1 GHz, sampling bandwidth is required to be higher than 2 GHz. However, the high-speed ADC with high sampling bandwidth has extremely high production complexity and costs, thereby restricting the development of the direct radio frequency receiver.
Therefore, how to enable an operating bandwidth of a receiver to reach the GHz magnitude without increasing costs and production complexity of the receiver is an urgent problem to be solved at present.